1. The Field of the Invention
The present invention relates to the field of electrosurgical probes and procedures for performing endoscopic thermal capsullorhaphy. In particular, the invention relates to electrosurgical probes and methods for locating and protecting the axillary nerve while performing arthroscopic thermal capsullorhaphy on the human shoulder.
2. The Prior State of the Art
The joint of the human shoulder provides the greatest range of motion of all the joints in the human body. However, when ligaments of the shoulder become stretched or damaged the shoulder can suffer from a condition known as shoulder instability, which can significantly limit the function of the shoulder. Shoulder instability can result from a violent injury that causes the shoulder to dislocate, or by a repetitive injury that stretches the ligaments of the shoulder over a period of time. Shoulder instability, if not cured, may cause chronic pain, arthritis, and loss of function.
Shoulder instability can sometimes be treated with rehabilitation. However, if rehabilitation is not successful or appropriate then surgery may be required. Surgery generally involves the tightening of lax and over-stretched capsular ligaments. Some surgical techniques, referred to as xe2x80x9ccapsular shift procedures,xe2x80x9d tighten and generally reconstruct the capsular ligaments of the shoulder.
Capsular shift procedures can be performed by open surgery or by arthroscopic surgery. Open surgery often results in greater post-operative pain and requires more extensive rehabilitation than arthroscopic surgery. Accordingly, as arthroscopic techniques continue to develop, they are increasingly chosen as the preferred method in the treatment of shoulder instability.
One recent advance in arthroscopic surgery, which is known as thermal capsullorhaphy, offers distinct advantages over capsular shift procedures and other similar techniques because it does not require the surgical reconstruction of the ligament capsules. This technique, which is also known as xe2x80x9cthermal capsulorraphy,xe2x80x9d xe2x80x9cthermal capsular shrinking,xe2x80x9d xe2x80x9cradiofrequency thermal shrinking,xe2x80x9d and xe2x80x9cthermal capsular shift,xe2x80x9d involves the non-contact shrinking of the capsular ligaments by heating the collagen fibers within the capsular ligaments with a radiofrequency probe (electrode) operating in either a bipolar or monopolar mode.
One problem associated with thermal capsullorhaphy, however, is that the temperature required to shrink the capsular ligaments can cause severe nerve damage. In particular, nerves have been shown to sustain irreversible injury at temperatures exceeding 55xc2x0 C., yet the minimum temperature required to shrink collagen and the capsular ligaments is known to be approximately 65xc2x0 C., with actual procedural temperatures approaching 100xc2x0 C.
Of particular interest is the axillary nerve, also known as the circumflex nerve, which passes directly beneath the inferior gleno-humeral capsular ligament of the shoulder, placing it at risk for thermal injury during thermal capsullorhaphy. Temporary injury to the axillary nerve, also known as axillary neuropraxia, as well as permanent thermal injury to the axillary nerve, are possible consequences of thermal capsullorhaphy because the intraarticular anatomic landmarks defining the course of the axillary nerve are vague, thereby making it difficult to identify and to avoid applying heat to the regions of tissue where the nerve is proximate the capsular ligaments. Although the temperatures that are applied to the capsular ligaments during thermal capsullorhaphy decrease exponentially with tissue depth, temperatures in excess of 55xc2x0 C. can easily be achieved at the minimal depths where the axillary nerve is located proximately to the capsular ligaments. Compounding this problem is the fact that the measured distance between the axillary nerve and the capsule ligaments in cadaveric specimens varies widely, suggesting that thermal capsullorhaphy creates a greater risk of axillary nerve injury for certain shoulders than for others.
Axillary neuropraxia and permanent damage to the axillary nerve can be avoided by using nerve stimulating devices to stimulate the axillary nerve and to identify the high-risk regions where the axillary nerve is extremely close to the capsular ligaments. The high-risk regions can then be avoided so that the axillary nerve is not overheated during the procedure. Existing nerve stimulating devices, typically used to identify nerves to be anesthetized, emit direct current (xe2x80x9cDCxe2x80x9d) pulses that stimulate motor nerves such as the axillary nerve. When a motor nerve is stimulated, it causes the muscles supplied by the nerve to contract. The visual observation of stimulating the axillary nerve, for example, is a physical jump or movement of the deltoid muscle.
Existing nerve stimulating devices, however, are not suitable for arthroscopic procedures. Arthroscopic procedures require the surgical site to be filled with a saline solution, which is highly conductive and which diffuses the DC energy before it can stimulate the axillary nerve, thereby making it difficult to identify and locate the high-risk regions of the capsular ligament that should be avoided during thermal capsullorhaphy.
Some existing RF electrodes are configured with temperature sensors located in the tip of the electrode for controlling the temperatures that are generated by the electrode. The temperature sensor in effect measures existing local surface temperatures and controls the RF energy that is applied by the electrode to the capsular ligaments. The benefit of temperature sensor electrodes in protecting the axillary nerve, however, is extremely limited. In particular, these electrodes are unable to identify the high-risk regions where the axillary nerve passes the capsular ligaments.
Accordingly, there is presently a need in the art for improved methods and devices that are able to locate the high-risk regions of the capsular ligaments during arthroscopic thermal capsullorhaphy in order to reduce the risk of axillary neuropraxia.
The present invention is directed to improved apparatus and methods for protecting the axillary nerve during thermal capsullorhaphy. In particular, the present invention is directed to systems comprising improved radiofrequency (RF) electrosurgical devices and methods for identifying and avoiding regions of the capsular ligaments that are in extremely close proximity to the axillary nerve, thereby reducing the risk of axillary neuropraxia or permanent damage to the axillary nerve while performing arthroscopic thermal capsullorhaphy. The apparatus and methods of the invention utilize what is known in the art as a coagulation or xe2x80x9ccoagxe2x80x9d RF waveform to stimulate and locate the axillary nerve preparatory to, or during, thermal capsullorhaphy.
The systems of the invention utilize intraoperative electrical stimulation of the axillary nerve as the means of identifying the anatomically xe2x80x9chigh-riskxe2x80x9d regions of the capsular ligaments that should be avoided during the thermal capsullorhaphy procedure. By avoiding the high-risk regions it is possible to minimize the likelihood of causing thermal damage to the axillary nerve.
According to one embodiment, an RF electrosurgical probe is electrically connected to a standard electrosurgical generator that is capable of producing RF energy having a coag waveform. The electrosurgical probe is equipped with a tip for dispensing the RF energy and a power cord that supplies RF energy from the generator. The probe may optionally include different activation switches depending on whether one wishes to shrink ligament tissue or perform nerve stimulation.
The electrosurgical probe can operate in a nerve stimulation mode and a tissue shrinkage mode. In the nerve stimulation mode, a quantity of RF energy is emitted from the electrosurgical probe that at least indirectly causes a nerve within a nerve stimulation zone to be stimulated, but which is insufficient to cause thermal damage to the nerve. The nerve stimulation zone is the area directly around the tip of the probe that receives a sufficiently strong stimulation signal to stimulate a nerve
In the tissue shrinkage mode, RF energy is continuously emitted from the tip of the electrosurgical probe so as to thermally shrink tissue in a tissue shrinkage zone surrounding the tip of the electrosurgical probe. The tissue shrinkage zone is essentially the area surrounding the tip of the electrosurgical probe that receives sufficient RF energy to cause tissue to thermally shrink.
In one embodiment, a stimulation signal comprises electrical noise that is a byproduct of RF energy having a coag waveform. The present invention enables a surgeon to identify high-risk regions where the axillary nerve passes in close proximity to the inferior gleno-humeral ligament by applying the stimulation signal to a treatment region where shoulder tissue is intended to be shrunk. The stimulation signal is applied in short bursts to stimulate the axillary nerve and to identify the high-risk regions of the capsular ligament, usually limited in size to about one square centimeter, that are located within such close proximity to the axillary nerve that thermally shrinking at those regions would likely cause thermal damage to the axillary nerve. Stimulating a nerve, such as the axillary nerve, can be accomplished according to the invention, even in a saline environment, such as during endoscopic surgery.
In one preferred embodiment, the stimulation signal is applied by the electrosurgical probe, in a nerve stimulation mode, at discrete location points over the entire area of treatment region where shoulder tissue is intended to be shrunk, thereby identifying any high-risk regions that should be avoided during thermal capsullorhaphy. Once the entire treatment region has been prospected for high-risk regions, the electrosurgical probe is used to emit high frequency energy having a coag or a cut waveform to heat and contract the collagen fibers of the tissue within the treatment region. Any high-risk regions are avoided during this step, thereby protecting the axillary nerve from thermal damage.
According to another embodiment, the stimulation signal is applied by the electrosurgical probe, in a nerve stimulation mode, to shoulder tissue at a small region and if the axillary nerve is not stimulated at that region then RF energy is applied by the electrosurgical probe, in a tissue shrinkage mode, to the shoulder tissue within that region until the shoulder tissue is heated to a sufficient temperature to cause thermal shrinking. The tip of the electrosurgical probe is then move to a new small region and the process is repeated. If the axillary nerve is stimulated at a given region, then the shoulder tissue at that region is passed over and not directly heated with RF energy.
It should be appreciated that the present invention generally enables a surgeon to prospect for a nerve, such as the axillary nerve, using an RF electrode employing a coag waveform that is generated from a standard electrosurgical generator. In so doing, the invention generally minimizes the risk of axillary nerve injury during thermal capsullorhaphy.
These and other features and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by practicing the invention as set forth below.